linux-kernel - Re: [PATCH V3 0/5] cpufreq: Record stats with fast-switching

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Date:   Mon, 5 Oct 2020 15:25:28 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Ben Segall <bsegall@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Lukasz Luba <lukasz.luba@....com>, cristian.marussi@....com,
        Sudeep Holla <sudeep.holla@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 0/5] cpufreq: Record stats with fast-switching

On Mon, Oct 5, 2020 at 9:56 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> Hi,
>
> We disabled recording cpufreq stats when fast switching was introduced
> to the cpufreq core as the cpufreq stats required to take a spinlock and
> that can't be allowed (for performance reasons) on scheduler's hot path.
>
> Here is an attempt to get rid of the lock and bring back the support.
>
> V2->V3:
> - Use READ/WRITE_ONCE() for reset-time as well.
> - Use unlikely for few conditionals in the hot path.
> - Better changelogs.
> - Rebase changes.
>
> V1-V2:
> - Use READ_ONCE/WRITE_ONCE instead of atomic in the first patch.
>
> --
> Viresh
>
> Viresh Kumar (5):
>   cpufreq: stats: Defer stats update to
>     cpufreq_stats_record_transition()
>   cpufreq: stats: Remove locking
>   cpufreq: stats: Mark few conditionals with unlikely()
>   cpufreq: stats: Enable stats for fast-switch as well
>   cpufreq: Move traces and update to policy->cur to cpufreq core
>
>  drivers/cpufreq/cpufreq.c        | 11 ++++
>  drivers/cpufreq/cpufreq_stats.c  | 89 ++++++++++++++++++++------------
>  kernel/sched/cpufreq_schedutil.c | 12 +----
>  3 files changed, 69 insertions(+), 43 deletions(-)
>
> --

The entire series applied as 5.10 material with some minor changelog
edits in patch [1/5], thanks!